Vishwas,

I guess (b) Is the cleaner approach but I am not fully understanding product mix. The REST style is {resource}/{resourceIdentifier} -  you can have {resource}/{resourceIdentifier}/{subresource}/{subresourceIdentifier} - for actions or complex functions we tend to sweep this behind the '?' as mentioned in the ApiGee document referenced in API docs.

On product mix - What is the purpose of this fuctionality? Why is it needed by MFIs? I know its in mifos but just trying to understand again why its useful.